1. Field of the Invention
The present invention relates to a continuously variable transmission which provides a wider range of input/output speed ratios than does a conventional continuously variable speed-change unit, by combining a toroidal-type continuously variable speed change unit and a planetary gear mechanism with torque circulation.
2. Description of the Related Art
A continuously variable transmission which includes a toroidal-type continuously variable speed change unit and has all of its components arranged on a single axis is disclosed WO Publication WO03/100295A1. As shown in FIG. 6(a), this continuously variable transmission 1 includes a toroidal-type continuously variable speed change unit 5, a planetary gear mechanism 6, a counter gear mechanism 7, and a Low/High switching mechanism 10, all of which are arranged on a single axis between an input shaft 12 and an output shaft 13. The toroidal-type continuously variable speed change unit 5 includes input discs 2 and an output disc 3, as well as rollers 4 arranged between these discs such that the radial position of contact with the discs can be changed. The planetary gear mechanism 6 has a carrier C1 on which three pinions P1, P2, P3 are arranged axially spaced. The counter gear mechanism 7 has a carrier C2 on which two pinions P4, P5 are arranged axially spaced. The Low/High switching mechanism 10 includes a Low brake L that can be engaged to hold output side sun gear S4 of the counter gear mechanism against rotation, and a High clutch H interposed between a second sun gear (i.e., a High mode output gear) S2 of the planetary gear unit and the output shaft 13.
Accordingly, when the continuously variable transmission 1 is in a Low mode in which the Low brake L is engaged and the High clutch H is released, rotation of the carrier C1 into which rotation is directly input from the input shaft 12 combines, in the planetary gear mechanism 6, with the rotation of an input side sun gear S1, the direction of which has been reversed and the speed of which has been changed, via the continuously variable speed change unit 5. This combined rotation is then output to a Low mode output gear (i.e., a third sun gear) S3. The rotation of the output gear S3 is then reversed and output to the output shaft 13.
The Low/High switching mechanism 10 may alternatively include a Low clutch L interposed between the carrier C2 and the output shaft 13, as shown in FIG. 6(b), and a High clutch H interposed between the second sun gear S2 of the planetary gear unit and the output shaft 13 like that described above.
In the continuously variable transmission shown in FIG. (6(a), the three pinions P1, P2, P3 of the planetary gear mechanism 6 are axially aligned in series. In addition, the two pinions P4, P5 of the counter gear mechanism 7 are also axially aligned. As a result, the continuously variable transmission has a long axial dimension.